Is it possible to get a labeled image from a binary image using OpenCV with an in-built C API

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alalek is one of OpenCV Team says in one response for a bug the following c API Bug:

"OpenCV is a C++ library now and actively uses C++ features, like exceptions and so on. Direct support for C compilers has been dropped some years ago, so you should not create C applications using OpenCV. "C-API" is not supported and should be removed totally (but we have a lack of resources to port this legacy C code to C++, so some of this code still exists right now). Also huge part of fresh OpenCV functionality is missing in "C-API". There is no plan to fix this in OpenCV directly. If you want to use OpenCV from C application code you need to find some implementation of C bindings which wraps OpenCV C++ functionality (al least these bindings should catch exceptions and return exit codes for user application)."

i think if you want to build c application using openCV dierectly you will lose the support from OpenCV Team , they will advice you to port to c++.

The c wrapper is my the advice for you , may be others have another advice for you.

... purely in C and without any wrappers, is it possible ?

No, it isnt. doing your own C wrapper might be your best bet:

// my_api.h (w/o any opencv headers)

extern "C" {
    int funny( void *there_be_pixels, int w, int h, int type );
}

// my.cpp (you'll have to compile it as c++, seperately from your other C code)

#include "opencv2/opencv.hpp"
#include "my_api.h"

int funny(void *there_be_pixels, int w, int h, int type)
{
    cv::Mat m(h, w, type, (char*)there_be_pixels);
    // do your c++ processing
}

what you should not try is, to use the legacy IplImage based api - i't s dead, does not give you a real 'watershed', also you're only writing more unwanted legecay code this way.